Field of the Invention
The present invention relates to an implant fixture used during a prosthesis treatment, and more particularly, to an implant fixture for preventing bone resorption and bone compression by minimizing stress on a hard portion of bone tissue.
Description of the Related Art
A screw type of fixture used in dentistry is inserted into bone tissue to form an artificial tooth root. When a fixture is inserted into bone tissue and combined with peripheral bone tissue, an abutment is coupled onto the fixture, and a prosthesis, which is an artificial tooth, is connected to the abutment. Such a fixture is made of a metal or the like fusible with peripheral bone tissue, has screw threads which are formed from an upper end to a lower end of an outer circumferential surface of a body portion of the fixture, and is used as a fixing member for fixing an orthopedic prosthesis as well as a dental prosthesis to a bone.
Meanwhile, bone tissue into which a fixture is inserted and implanted includes a cortical bone and a cancellous bone. The cancellous bone is relatively soft bone tissue of a bone, and the cortical bone is harder than the cancellous bone and is generally formed as a relatively thin film surrounding the cancellous bone. When the fixture is inserted into bone tissue, a length of a portion in contact with the cancellous bone is greater than that of a portion in contact with the cortical bone.
An implant fixture 10 used in a dental treatment in the related art includes a head portion 12 having a hole into which a rotary tool is inserted in the center thereof, and a body portion 14, which is provided to be tapered below the head portion 12 and has screw threads 16 which are formed on an outer circumferential surface thereof, as illustrated in FIG. 1.
Bone resorption is one of problems occurring when the implant fixture 10 in the related art is inserted into an alveolar bone of a human body. Bone resorption refers to a phenomenon in which bone tissue into which a fixture is implanted is degraded while an amount of peripheral bone tissue is reduced. Such bone resorption may inhibit stability of a prosthesis by weakening a fixing force of the fixture and may result in damage to the prosthesis.
Biological causes of the bone resorption have not yet been clearly identified. However, since stress acting on bone tissue adjacent to a fixture is non-uniformly distributed, bone resorption has been recognized as being promoted by both over stimulation and low stimulation due to stress concentration. Therefore, it is necessary to uniformly distribute stress in order to prevent bone resorption and promote osseointegration between a fixture and bone tissue.
That is, since the implant fixture 10 in the related art concentrates relatively more stress on a cortical bone, which is a hard portion of bone tissue, bone resorption occurs more frequently in the cortical bone. However, as a pitch of the screw thread 16 and a difference between an outer diameter of the screw thread 16 and an inner diameter thereof (an outer diameter of a screw valley) are increased, partial concentration of stress on an individual screw thread is increased while a fixing force of the fixture is increased.
Since the screw threads 16 of the implant fixture 10 in the related art are formed to be the same as those of a triangular screw or a trapezoidal screw throughout the body portion 14, an imbalance of overall stress in which stress is relatively concentrated on the cortical bone compared to the cancellous bone occurs. Since bone resorption is caused much more in the cortical bone than in the cancellous bone due to such an imbalance of stress on the entire implant fixture 10 in the related art, the bone resorption in the cortical bone adversely affects an appearance of a prosthesis as well as a stability of the prosthesis. Therefore, a demand for reducing the stress concentrated on the cortical bone or preventing the bone resorption in the cortical bone by distributing the stress to the cancellous bone has arisen.